Vitamin B12 and Folate Administration on Homocysteine Concentrations After Nitrous Oxide Anesthesia (Mini-VINO)

Influence of Preoperative Vitamin B12 and Folate Administration on Homocysteine Concentrations After Nitrous Oxide Anesthesia

The goal of this study is to find out if giving intravenous B-vitamins before general anesthesia with nitrous oxide prevents the increase in homocysteine, a metabolite that has been linked to cardiovascular complications.

Patients will be randomized into the following arms: Arm A: patients will receive N2O (60% N2O/40% O2) in an open-label fashion during surgery and vitamin supplementation (vitamin B12, 1 mg, and folate, 5 mg) before surgery. Arm B: patients will receive N2O 60% N2O/40% O2) in an open-label fashion during surgery and placebo before and after surgery. Arm C: patients will not receive N2O, vitamin supplementation, or placebo during/before surgery. Patients in this arm will not be randomized. Patients will have blood drawn (total of 1-2 teaspoons over 3 days). We will take these samples before their surgery, when their surgery is completed, and in the morning of post-operative day 1. We will be checking their troponin I and troponin T, homocysteine, Vitamin B12, and folate levels. We will also perform a 12-lead EKG. Before and after surgery for patients in Arm A or B, will receive either vitamin B12 (1 mg) and folic acid (5 mg) (or placebo) added to their IV infusion. We also plan to use a non-invasive test known as a nerve conduction study to measure the function of their nerve system. Briefly, 2 small electrodes are attached to their skin over a nerve and, like an EKG, faint electrical pulses are generated and recorded. A typical nerve conduction measurement lasts about 10 minutes. After the patients surgery we will do genetic testing of MTHFR genotype. All study samples have been collected. Of note: there were no secondary outcomes.

IV vitamin B12 (cyanocobalamin) 1 mg, single administration over 30 min. IV folic acid, 5 mg, single administration over 30 min. Both diluted in 250 ml normal saline.

Difference between baseline (pre-operative) and peak postoperative (i.e., maximum of postoperative value obtained within 30 minutes after anesthesia end time and morning of post-operative day 1) tHcy concentration . Of note: there were no secondary outcomes.

Inclusion Criteria: Adult patients scheduled for elective surgery with expected duration > 2 hours Healthy patients undergoing moderate surgery where the use of N2O is unproblematic Exclusion Criteria: Contraindication against N2O (pneumothorax, mechanical bowel obstruction, middle ear occlusion, laparoscopic surgery, raised intracranial pressure) Patients requiring supplemental oxygen Urgent or emergent surgery Patients with vitamin B12 or folate deficiency or megaloblastic anemia Patients with seizure disorder (epilepsy) Allergy or hypersensitivity against IV cobalamin or folate Patients with Leber's disease (hereditary optic nerve atrophy) Patients taking supplemental vitamin B12 or folate

Nagele P, Zeugswetter B, Wiener C, Burger H, Hupfl M, Mittlbock M, Fodinger M. Influence of methylenetetrahydrofolate reductase gene polymorphisms on homocysteine concentrations after nitrous oxide anesthesia. Anesthesiology. 2008 Jul;109(1):36-43. doi: 10.1097/ALN.0b013e318178820b.

Nagele P, Zeugswetter B, Eberle C, Hupfl M, Mittlbock M, Fodinger M. A common gene variant in methionine synthase reductase is not associated with peak homocysteine concentrations after nitrous oxide anesthesia. Pharmacogenet Genomics. 2009 May;19(5):325-9. doi: 10.1097/FPC.0b013e328328d54c.

Myles PS, Chan MT, Kaye DM, McIlroy DR, Lau CW, Symons JA, Chen S. Effect of nitrous oxide anesthesia on plasma homocysteine and endothelial function. Anesthesiology. 2008 Oct;109(4):657-63. doi: 10.1097/ALN.0b013e31818629db.